Is there any truth to this. I read some where that when your fermentation starts to slow, you can gently rock yopur primary and slosh the wort to the sides of the bucket. This gets any yeast that is stuck in the krausen on the sides to go back into the wort

Well, you don't want that krausen ring back in your beer. That stuff is bitter and nasty.

What they are probably referring to is in a stuck fermentation (when the fermentation stalls before it's finished), you can gently swirl or rock to rouse the yeast that has fallen to the bottom. This really isn't necessary 99% of the time, but occasionally you use a highly flocculant yeast strain that falls out before finishing fermentation, or the fermenter gets too cold and the yeast drops out before finishing the job.

In a regular fermentation, though, you don't want to do that. You want the krausen ring to stay put, and you want the yeast cake and trub at the bottom, so that you can siphon off the good, clear beer.

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I've had good luck with getting stuck fermentations started back up with a little shaking/rocking. Usually, just the agitation you get from moving the carboy to a warmer location does the trick though.